The present invention relates generally to a drive guide system for use in an automotive vehicle, which system is to be employed during driving to show the direction and remaining distance to the destination. More particularly, the present invention relates to error correction and error monitoring for a magnetic compass detecting the terrestrial magnetism and thereby detecting the vehicle driving direction.
While driving an automotive vehicle, information concerning the direction and approximated remaining distance to the destination and so forth would be helpful to the vehicle driver. In order to provide such information, various pilot systems or drive guide systems have recently been developed. These drive guide systems are provided with sensors for detecting vehicle direction with respect to the destination, such as a gyrocompass, magnetic compass or the like. Some of such drive guide systems are provided with a magnetic compass which detects the geomagnetic field, i.e. terrestrial magnetism. Application of such a magnetic compass to an automotive drive guide system causes a problem in that since the vehicle body and vehicle device per se create a static magnetic field or some vehicle devices include magnetic materials, interference may disturb the magnetic compass and result in errors in detection of the directions. Such errors in direction detection will influence the displayed driving orientation or the direction toward the destination with respect to the driving direction or vehicle position. Therefore, correction of the detected direction by detecting the error angle of the magnetic compass is essential to keep the system effective.
If the error of the compass is due only to the interfering magnetic noise created by the vehicle per se and assuming the magnitude of the interfering magnetic noise does not change, an initial adjustment upon assembly of the vehicle may prevent the above erroneous operation of the magnetic compass. However, it is possible that the magnitude of the magnetic noise may change because the vehicle is often subjected to magnetic forces when passing through relatively strong magnetic fields, such as a railway or relatively high voltage cables. Therefore, even though initial interference of detection of the direction can be eliminated by the initial adjustment, there is rather high possibility that the magnetic compass detects the direction of the terrestrial magnetism and thus of the vehicle orientation in error to cause failure of the system operation.